Positive-working photoresist composition

ABSTRACT

Proposed is a novel positive-working photoresist composition of the chemical sensitization type capable of giving a finely patterned resist layer having an excellent cross sectional profile even for a discretely isolated pattern with high sensitivity and high resolution. The composition comprises, besides (a) a compound generating an acid by the irradiation with actinic rays, (b) a resinous ingredient capable of being imparted with increased solubility in an alkaline developer solution in the presence of an acid and (c) an organic solvent which is a ketone, ether or ester as the basic ingredients of the chemical sensitization type photoresist compositions, (d) an N,N-dialkyl carboxylic acid amide such as N,N-dimethyl formamide and N,N-dimethyl acetamide in a specified proportion relative to the component (b).

BACKGROUND OF THE INVENTION

The present invention relates to a novel positive-working photoresistcomposition or, more particularly, to a chemical sensitization-typepositive-working photoresist composition in the form of a solutioncapable of giving a finely discrete patterned resist layer having anexcellent cross sectional profile with high sensitivity to actinic raysand high pattern resolution.

As is known, the photolithographic patterning process by utilizing apositive-working photoresist composition is widely practiced in themanufacture of various kinds of semiconductor devices such as ICs, LSIsand the like. The photolithographic patterning work using apositive-working photoresist composition is performed by first forming alayer of the photoresist composition on the surface of a substrate suchas a semiconductor silicon wafer and the photoresist layer is exposed toactinic rays such as ultraviolet light patternwise through a photomaskbearing a desired device pattern to form a latent image of the pattern,which is then developed by dissolving away the resist layer in theultraviolet-exposed areas with a developer solution leaving a patternedresist layer to serve as a protective resist in the subsequent treatmentof the substrate surface such as etching. Positive-working photoresistcompositions used in the above described photolithographic patterningtypically have a formulation comprising an alkali-soluble novolac resinas a film-forming agent and a quinone diazide group-containing compoundas a photosensitive ingredient uniformly dissolved in an organicsolvent.

Along with the trend in the semiconductor technology toward a highdegree of integration in the semiconductor devices increasing year byyear, the manufacturing process of VLSIs and the like requires anextremely high fineness of the photolithographic patterning workssometimes in the ranges of the sub-micron order or quarter-micron order.This requirement for the high fineness of patterning to be accomplishednaturally depends on the performance of the photoresist composition andalso on the effective wavelength of the actinic rays, e.g., ultravioletlight. For example, the wavelength range of the ultraviolet light usedin the photolithographic patterning work is under a trend of decreasingfrom the g-line and i-line to deep-ultraviolet light and excimer laserbeams such as KrF laser beams as an important light source in thistechnology.

Chemical sensitization-type photoresist compositions as a class of thephotoresist compositions are now under active development works becausean ultraviolet light of a shorter wavelength such as deep ultravioletand excimer laser beams can be utilized for the patternwise exposurethan for the conventional photoresist compositions of the abovementioned type comprising a novolac resin and a quinone diazidegroup-containing compound so as to provide a possibility of obtaining ahigh resolution and a high sensitivity by virtue of the catalyticreaction and chain reaction of a quantum yield larger than 1 by the acidgenerated by the irradiation with actinic rays.

Since the chemical sensitization-type photoresist composition has beendeveloped with an object to comply with the requirement for an extremelyfine patterning of a width of 0.3 μm or even finer, an attention isrecently directed to the cross sectional profile of discrete or isolatedresist patterns. For example, it is sometimes the case that, when apatterned resist layer has a cross sectional profile standing on thesubstrate surface with a downwardly decreasing width toward thesubstrate surface, the patterned resist layer eventually falls down onthe substrate surface. This phenomenon is a very serious problem to besolved when a chemical sensitization-type photoresist composition is tobe used for the photolithographic patterning of extreme fineness.

SUMMARY OF THE INVENTION

The present invention accordingly has an object, in view of the abovedescribed situations, to provide a chemical sensitization-typepositive-working photoresist composition in the form of a solutioncapable of giving an extremely fine discretely patterned resist layerhaving excellently orthogonal cross sectional profile with highsensitivity and high resolution.

Thus, the positive-working photoresist composition of the inventioncomprises, in the form of a uniform solution:

(a) a compound capable of generating an acid by the irradiation withactinic rays;

(b) a resinous compound capable of being imparted with an increasedsolubility in an aqueous alkaline solution in the presence of an acid;

(c) an organic solvent selected from the group consisting of ketonecompounds, ether compounds and ester compounds; and

(d) an N,N-dialkyl carboxylic acid amide in an amount in the range from0.1 to 5% by weight based on the amount of the component (b).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As is described above, the essential ingredients in the positive-workingphotoresist composition of the invention include the components (a) to(d) defined above. The component (a) is a compound capable of releasingan acid by the irradiation with actinic rays, referred to as theacid-generating agent hereinafter, which is not particularly limitativeand can be selected from those compounds used in conventional chemicalsensitization-type photoresist compositions including:

i) bis(sulfonyl) diazomethane compounds such as bis(p-toluenesulfonyl)diazomethane, methylsulfonyl p-toluenesulfonyl diazomethane,cyclohexylsulfonyl 1,1-dimethylethylsulfonyl diazomethane,bis(1,1-dimethylethylsulfonyl) diazomethane, bis(1-methylethylsulfonyl)diazomethane, bis(cyclohexylsulfonyl) diazomethane,bis(2,4-dimethylphenylsulfonyl) diazomethane, bis(4-ethylphenylsulfonyl)diazomethane, bis(3-methylphenylsulfonyl) diazomethane,bis(4-methoxyphenylsulfonyl) diazomethane, bis(4-fluorophenylsulfonyl)diazomethane, bis(4-chlorophenylsulfonyl) diazomethane,bis(4-tert-butylphenylsulfonyl) diazomethane and the like;

ii) sulfonyl carbonyl alkane compounds such as2-methyl2-(p-toluenesulfonyl) propiophenone,2-cyclohexylcarbonyl2-(p-toluenesulfonyl) propane, p-methylthiophenyl(1methanesulfonyl-1-methyl)ethyl ketone,2,4-dimethyl-2(p-toluenesulfonyl)pentan-3-one and the like;

iii) sulfonyl carbonyl diazomethane compounds such as p-toluenesulfonylcyclohexylcarbonyl diazomethane,1-diazo1-methylsulfonyl-4-phenyl-2-butanone, cyclohexylcarbonylcyclohexylsulfonyl diazomethane,1-cyclohexylsulfonyl-1diazo-3,3-dimethyl-2-butanone,1-diazo-1-(1,1-dimethylethylsulfonyl)-3,3-dimethyl-2-butanone,1-acetyl-1-(1methylethylsulfonyl) diazomethane,1-diazo-1-(p-toluenesulfonyl)-3,3-dimethyl-2-butanone,1-benzenesulfonyl-1-diazo3,3-dimethyl-2-butanone,1-diazo-1-(p-toluenesulfonyl)-3methyl-2-butanone,2-diazo-2-(p-toluenesulfonyl)cyclohexyl acetate,2-benzenesulfonyl-2-diazo tert-butyl acetate, 2-diazo-2-methanesulfonylisopropyl acetate, 2-benzenesulfonyl-2-diazo cyclohexyl acetate,2-diazo-2-(p-toluenesulfonyl) tert-butyl acetate and the like;

iv) nitrobenzyl sulfonate compounds such as 2-nitrobenzylp-toluenesulfonate, 2,6-dinitrobenzyl p-toluenesulfonate,2,4-dinitrobenzyl 4-trifluoromethylbenzenesulfonate and the like; and

v) esters of a polyhydroxy compound and an aliphatic or aromaticsulfonic acid such as pyrogallol methanesulfonates, pyrogallolbenzenesulfonates, pyrogallol p-toluenenesulfonates, pyrogallolp-methoxybenzenesulfonates, pyrogallol mesitylenesulfonates, pyrogallolbenzylsulfonates, esters of an alkyl gallate and methane sulfonic acid,esters of an alkyl gallate and benzene sulfonic acid, esters of an alkylgallate and p-toluene sulfonic acid, esters of an alkyl gallate and4-methoxybenzene sulfonic acid, esters of an alkyl gallate andmesitylene sulfonic acids, esters of an alkyl gallate and benzylsulfonicacid and the like. The alkyl group in the above mentioned alkyl gallatespreferably has 15 or a smaller number of carbon atoms and octyl andlauryl groups are particularly preferred. Besides the above named fiveclasses i) to v), onium salts such as bis(4-tertbutylphenyl) iodoniumtrifluoromethane sulfonate, triphenylsulfonium trifluoromethanesulfonate and the like can also be used as the component (a). Among theabove named acid-generating agents, bis(sulfonyl) diazomethane compoundsare preferable, of which quite satisfactory results can be obtained withbis(cyclohexylsulfonyl) diazomethane or bis(2,4-dimethylphenylsulfonyl)diazomethane. These acid-generating agents can be used either singly oras a combination of two kinds or more according to need.

The component (b) in the inventive photoresist composition is a resinouscompound capable of being imparted with an increased solubility in anaqueous alkaline solution in the presence of an acid. Such a resin isknown in the art of chemical sensitization-type photoresist compositionsand any of those conventionally used in such compositions can be usedhere without particular limitations. Examples of suitable resinouscompounds include poly(hydroxystyrene) resins of which at least a partof the hydroxy groups are substituted by protective groups exemplifiedby tertbutoxycarbonyloxy group, tert-butyloxy group andtertamyloxycarbonyloxy group as well as acetal groups such asalkoxyalkoxy groups, tetrahydropyranyloxy group and tetrahydrofuranyloxygroup.

The poly(hydroxystyrene) resin of which a part of the hydroxy groups aresubstituted by the above named protective groups can be obtained by thecopolymerization of a hydroxystyrene and a substituted hydroxystyreneor, alternatively, by introducing the protective groups into apoly(hydroxystyrene) by a polymer reaction. Various kinds of suchsubstituted poly(hydroxystyrene) resins are known including a copolymerof 4-hydroxystyrene and a tert-butoxycarbonyloxy styrene disclosed inJapanese Patent Kokai 2-209977, copolymer of 4-hydroxystyrene and4-tetrahydropyranyloxy styrene disclosed in Japanese Patent Kokai2-19847, copolymer of 4-hydroxystyrene and a tert-butoxy styrenedisclosed in Japanese Patent Kokai 2-62544, a poly(hydroxystyrene)substituted by acetal groups for a part of the hydroxy groups disclosedin Japanese Patent Kokai 3-282550, poly(hydroxystyrene) substituted byalkoxyalkoxy groups for a part of the hydroxy groups disclosed inJapanese Patent Kokai 5-249682 and the like. These partially substitutedpoly(hydroxystyrene) resins can be used either singly or as acombination of two kinds or more according to need. A preferablecombination of the partially substituted poly(hydroxystyrene) resins isa combination of a first resin which is a poly(hydroxystyrene)substituted for 10 to 60% of the hydroxy groups bytert-butoxycarbonyloxy groups and a second resin which is apoly(hydroxystyrene) substituted for 10 to 60% of the hydroxy groups bythe groups represented by the general formula

    ---O--CR.sup.1 R.sup.2 (OR.sup.3),                         (I)

in which R¹ is a hydrogen atom or a methyl group, R² is a methyl orethyl group and R³ is a lower alkyl group having, for example, 1 to 4carbon atoms.

The above mentioned substituent group represented by the general formula(I) is exemplified by 1-methoxyethoxy, 1-ethoxyethoxy,1-n-propoxyethoxy, 1-isopropoxyethoxy, 1-n-butoxyethoxy,1-isobutoxyethoxy, 1-(1,1-dimethylethoxy)-1-methylethoxy,1-methoxy-1-methylethoxy, 1-ethoxy-1methylethoxy,1-methyl-1-n-propoxyethoxy, 1-isobutoxy-1methylethoxy,1-methoxy-n-propoxy and 1-ethoxy-n-propoxy groups. Among the above namedsubstituent groups, 1-ethoxyethoxy group and 1-methoxy-n-propoxy groupare preferred in respect of the good balance between the respectivelyincreased sensitivity and resolution. When the component (b) is acombination of the above mentioned first and second poly(hydroxystyrene)resins, a preferable proportion of the first to the second is in therange from 10:90 to 70:30 by weight or, more preferably, from 20:80 to50:50 by weight. When an acid is released from the component (a) by theirradiation with actinic rays, the tert-butoxycarbonyloxy andethoxyethoxy groups are decomposed by the activity of the acid to suchan extent that a good balance is obtained between the solubilitybehavior of the resinous compound and the solubility-inhibiting power ofthe tert-butoxycarbonyloxy groups so as to accomplish high sensitivity,high resolution and high heat resistance of the composition. Theseadvantages cannot be fully exhibited when the blending proportion of thetwo types of the resins is outside of the above mentioned specificrange.

The above mentioned substituted poly(hydroxystyrene) resin of the firsttype can be obtained by a known substitution reaction oftert-butoxycarbonyloxy groups for a part of the hydroxy groups in apoly(hydroxystyrene) resin by using, for example, di-tert-butyldicarbonate and the like. The degree of substitution is in the rangefrom 10 to 60% or, preferably, from 20 to 50%. When the degree ofsubstitution is too low, the photoresist composition formulated withsuch a resin as a part of the component (b) cannot give a patternedresist layer having an excellently orthogonal cross sectional profilewhile, when the degree of substitution is too high, a decrease is causedin the sensitivity of the photoresist composition formulated with such aresin as a part of the component (b).

The above mentioned substituted poly(hydroxystyrene) resin of the secondtype can be obtained by a known substitution reaction of the groupsrepresented by the above given general formula (I) for a part of thehydroxy groups in a poly(hydroxystyrene) resin by using, for example,1chloro-1-ethoxy ethane, 1-chloro-1-methoxy propane and the like. Thedegree of substitution is in the range from 10 to 60% or, preferably,from 20 to 50%. When the degree of substitution is too low, thephotoresist composition formulated with such a resin as a part of thecomponent (b) cannot give a patterned resist layer having an excellentlyorthogonal cross sectional profile while, when the degree ofsubstitution is too high, a decrease is caused in the sensitivity of thephotoresist composition formulated with such a resin as a part of thecomponent (b).

It is preferable that the above described resinous ingredient as thecomponent (b) has a weight-average molecular weight in the range from3000 to 30000 as determined by the gel permeation chromatographic (GPC)method making reference to polystyrene resins having specified molecularweights. When the molecular weight of the resin is too low, the resistlayer formed from the composition would have inferior properties of thefilm while, when the molecular weight thereof is too high, a decrease iscaused in the solubility behavior of the resist layer in an aqueousalkaline solution resulting in a trouble in the development treatment.

The component (c) is an organic solvent which serves to dissolve theother ingredients of the composition to give a uniform solution. Thesolvent is selected from the group consisting of ketone compounds, ethercompounds and ester compounds including acetone, methyl ethyl ketone,cyclohexanone, methyl isoamyl ketone and 2-heptanone as the examples ofthe ketone compounds, monoacetate monoalkyl, e.g., monomethyl,monoethyl, monopropyl, monobutyl and monophenyl, ethers of a polyhydricalcohol such as ethyleneglycol, diethyleneglycol, propyleneglycol anddipropyleneglycol and mono- or dimethyl ether, mono- or diethyl ether,mono- or dipropyl ether and mono- or dibutyl ether and mono- or diphenylether of the above named polyhydric alcohols as well as dioxane as theexamples of the ether compounds and methyl lactate, ethyl lactate,methyl acetate, ethyl acetate, butyl acetate, methyl pyruvate, ethylpyruvate, methyl methoxypropionate and ethyl ethoxypropionate as theexamples of the ester compounds. These organic solvents can be usedeither singly or as a mixture of two kinds or more according to need.The amount of the organic solvent as the component (c) in the inventivephotoresist composition is, though not particularly limitative, in therange from 3 to 10 times by weight of the total amount of the components(a) and (b).

The amount of the acid-generating agent as the component (a) relative tothe component (b) is in the range from 1 to 20 parts by weight or,preferably, from 2 to 10 parts by weight per 100 parts by weight of thecomponent (b). When the amount of the component (a) is too small, thechemical sensitizing effect desired for this ingredient is insufficientnot to give a photoresist composition having high sensitivity while,when the amount of the component (a) is too large, a problem is causedin respect of the compatibility of the component (a) with the otheringredients not to give a uniform solution.

While the above described components (a), (b) and (c) are ratherconventional at least in the generic sense, the most characteristicfeature of the inventive photoresist composition consists in theformulation of a very unique ingredient which is an N,N-dialkylcarboxylic acid amide as the component (d). This compound is preferablyan N,N-dialkyl amide, each alkyl group having 1 to 4 carbon atoms, of alower carboxylic acid having 1 to 4 carbon atoms in a molecule inrespect of the effect on the improvement of the cross sectional profileof the discretely patterned resist layer. In particular, N,N-dimethylformamide and N,N-dimethyl acetamide are preferred as the component (d)though not particularly limitative thereto. These N,N-dialkyl carboxylicacid amides can be used either singly or as a combination of two kindsor more according to need. The amount of the component (d) in theinventive photoresist composition is in the range from 0.1 to 5% byweight or, preferably, from 0.5 to 3% by weight based on the amount ofthe component (b) from the standpoint of obtaining a good balancebetween the sensitivity of the composition and the cross sectionalprofile of the discretely patterned resist layer. When the amountthereof is too small, the effect of improvement would be insufficient onthe cross sectional profile of a discretely patterned resist layerwhile, when the amount thereof is too large, the sensitivity of thephotoresist composition is rather decreased without additionaladvantages by increasing the amount to exceed the above mentioned upperlimit.

It is of course optional that the inventive photoresist compositioncomprising the above described essential components (a) to (d) isfurther admixed with various kinds of known additives includingauxiliary resins, plasticizers and stabilizers to improve the filmproperties of the resist layer, coloring agents, surface active agentsand the like conventionally used in photoresist compositions each in alimited amount.

The procedure for the photolithographic patterning works by using theabove described photoresist composition of the invention is notparticularly different from that by using a conventionalpositive-working photoresist composition. For example, the inventivephotoresist composition in the form of a coating solution prepared fromthe above described essential and optional ingredients is uniformlyapplied to the surface of a substrate such as a semiconductor siliconwafer by using a suitable coating machine such as a spinner followed bydrying to give a photoresist layer on the substrate surface, which isthen exposed patternwise to actinic rays such as deep ultraviolet light,excimer laser beams and the like on a minifying projection exposuremachine through a pattern-bearing photomask to give a latent image ofthe pattern followed by a development treatment in an aqueous alkalinesolution such as a 1 to 10% by weight aqueous solution oftetramethylammonium hydroxide leaving the resist layer in the unexposedareas to give a patterned resist layer having fidelity to the maskpattern.

In the following, the positive-working photoresist composition of theinvention is described in more detail by way of examples, which,however, never limit the scope of the invention in any way. In thefollowing description, the term of "parts" always refers to "parts byweight".

EXAMPLE 1

A positive-working photoresist composition in the form of a solution wasprepared by uniformly dissolving, in 490 parts of propyleneglycolmonomethyl ether acetate, 100 parts of a 3:7 by weight mixture of afirst poly(hydroxystyrene) resin substituted by tert-butyloxycarbonyloxygroups for 39% of the hydroxy groups and having a weight-averagemolecular weight of 10000 and a second poly(hydroxystyrene) resinsubstituted by ethoxyethoxy groups for 39% of the hydroxy groups andhaving a weight-average molecular weight of 10000, 7 parts ofbis(cyclohexylsulfonyl) diazomethane and 2 parts of N,N-dimethylacetamide followed by filtration through a membrane filter of 0.2 μmpore diameter.

The thus prepared photoresist solution was applied to the surface of asemiconductor silicon wafer on a spinner followed by drying at 90° C.for 90 seconds to give a resist layer having a thickness of 0.7 μm asdried. The photoresist layer was exposed patternwise to ultravioletlight on a minifying projection exposure machine (Model NSR-2005EX8A,manufactured by Nikon Co.) to give an exposure dose stepwise increasedby 1 mJ/cm² increments followed by a post-exposure baking treatment byheating at 110° C. for 90 seconds and a development treatment for 65seconds at 23° C. in a 2.38% by weight aqueous solution oftetramethylammonium hydroxide, rinse treatment in running water for 30seconds and drying to give a discretely patterned resist layer of linewidth of 0.25 μm having an excellently orthogonal cross sectionalprofile as examined with a scanning electron microscope. Thephotosensitivity of the composition determined by the above describedexposure test was 38 mJ/cm².

EXAMPLE 2

The experimental procedure was substantially the same as in Example 1excepting a decrease of the amount of N,N-dimethyl acetamide from 2parts to 1 part. The orthogonality of the cross sectional profile of thethus obtained discretely patterned resist layer was as satisfactory asin Example 1. The photosensitivity of the composition was also about thesame as that in Example 1.

EXAMPLE 3

The experimental procedure was substantially the same as in Example 1excepting replacement of the N,N-dimethyl acetamide with the same amountof N,N-dimethyl formamide. The orthogonality of the cross sectionalprofile of the thus obtained discretely patterned resist layer was assatisfactory as in Example 1. The photosensitivity of the compositionwas also about the same as that in Example 1.

EXAMPLE 4

The experimental procedure was substantially the same as in Example 3excepting an increase of the amount of N,N-dimethyl formamide from 2parts to 3 parts. The orthogonality of the cross sectional profile ofthe thus obtained discretely patterned resist layer was as satisfactoryas in Example 1. The photosensitivity of the composition was also aboutthe same as that in Example 1.

EXAMPLE 5

The experimental procedure was substantially the same as in Example 1excepting replacement of the propyleneglycol monomethyl ether acetatewith the same amount of 2-heptanone. The orthogonality of the crosssectional profile was quite satisfactory in a discretely patternedresist layer having a width of 0.25 μm. The photosensitivity of thephotoresist composition was 40 mJ/cm².

EXAMPLE 6

The experimental procedure was substantially the same as in Example 1excepting replacement of the propyleneglycol monomethyl ether acetatewith the same amount of diethyleneglycol dimethyl ether. Theorthogonality of the cross sectional profile was quite satisfactory in adiscretely patterned resist layer having a width of 0.25 μm. Thephotosensitivity of the photoresist composition was 39 mJ/cm².

COMPARATIVE EXAMPLE

The experimental procedure was substantially the same as in Example 1excepting omission of the N,N-dimethyl acetamide in the formulation ofthe photoresist solution. The examination of the cross sectional profileof the patterned resist layer indicated that the discretely patternedresist layer fell down and lay on the substrate surface.

What is claimed is:
 1. A positive-working photoresist composition whichcomprises, in the form of a uniform solution:(a) a compound capable ofgenerating an acid by the irradiation with actinic rays; (b) a resinouscompound capable of being imparted with an increased solubility in anaqueous solution in the presence of an acid; (c) an organic solventselected from the group consisting of ketone compounds, ether compoundsand ester compounds; and (d) N,N-dimethyl formamide or N,N-dimethylacetamide in an amount in the range from 0.1 to 5% by weight based onthe amount of the component (b).
 2. The positive-working photoresistcomposition as claimed in claim 1 in which the component (a) is selectedfrom the group consisting of bis(sulfonyl) diazomethane compounds,sulfonylcarbonyl alkane compounds, sulfonylcarbonyl diazomethanecompounds, nitrobenzyl sulfonate compounds, esters of a polyhydroxycompound and an aliphatic or aromatic sulfonic acid and onium salts. 3.The positive-working photoresist composition as claimed in claim 2 inwhich the component (a) is bis(cyclohexylsulfonyl) diazomethane orbis(2,4-dimethylphenylsulfonyl) diazomethane.
 4. The positive-workingphotoresist composition as claimed in claim 1 in which the component (b)is a poly(hydroxystyrene) resin substituted for at least a part of thehydroxy groups by protective groups selected from the group consistingof tert-butoxycarbonyloxy group, tert-butyloxy group,tert-amyloxycarbonyloxy group and acetal groups.
 5. The positive-workingphotoresist composition as claimed in claim 4 in which thepoly(hydroxystyrene) resin is substituted for from 10% to 60% of thehydroxy groups by the protective groups.
 6. The positive-workingphotoresist composition as claimed in claim 5 in which the component (b)is a combination of a first poly(hydroxystyrene) resin substituted forfrom 10% to 60% of the hydroxy groups by tert-butoxycarbonyloxy groupsand a second poly(hydroxystyrene) resin substituted for from 10% to 60%of the hydroxy groups by the groups represented by the general formula

    --O--CR.sup.1 R.sup.2 (OR.sup.3),

in which R¹ is a hydrogen atom or a methyl group, R² is a methyl groupor ethyl group and R³ is a lower alkyl group having 1 to 4 carbon atoms,in a weight proportion in the range from 10:90 to 70:30.
 7. Thepositive-working photoresist composition as claimed in claim 4 in whichthe poly(hydroxystyrene) resin has a weight-average molecular weight inthe range from 3000 to
 30000. 8. The positive-working photoresistcomposition as claimed in claim 1 in which the amount of the component(a) is in the range from 1 to 20 parts by weight per 100 parts by weightof the component (b).
 9. The positive-working photoresist composition asclaimed in claim 1 in which the amount of the component (d) is in therange from 0.5 to 3% by weight based on the amount of the component (b).